The present invention relates to an apparatus for electrical stimulation, more particularly for the treatment of scoliosis with at least one channel for a pair of electrodes and an electrical circuit for adjusting the duration, amplitude and frequency of individual pulses as well as the time off between the individual pulses and the evolution in time of series of pulses, whereby the amplitude of the individual square pulses increases in an initial phase, then reaches a hold level and finally decreases again. Such an apparatus is known from the U.S. Pat. No. 4,326,534. Moreover, other embodiments of this apparatus are described in the two successive U.S. Pat. Nos. 4,342,317 and 4,408,609 of the same inventor.
Particularly in case of scoliosis, for which the above mentioned apparatus according to the invention is specifically provided, that is in case of spinal deformities which are characterized by lateral curvature and torsion of the spine, there is pathologic displacement of the pattern of muscular fibres which necessitates a particular respond by electrical stimulation for achieving a curvature correction. Recent researches have shown that in case of scoliosis the normal pattern of repartition of the muscular fibres with about 64% of tonus fibres and 36% of contraction fibres is displaced in favour of the tonus fibres. These tonus fibres, which have the task to maintain a certain condition of continuous tension in the musculature, are less influenced by the electrophysiological stimulation because their membrane-properties are modified. In this way, the patients have less contraction fibres at disposal, these fibres exhibiting a good reaction to electrophysiological stimulation excitations, thus being of decisive importance for the extent of the muscular effect on the curvature of the spine. Recent experiments on animals have shown that it is possible by high frequency stimulation to change backwards the number of the tonus fibres, thus permitting correction of the disturbed balance in favour of the tonus fibres.
Principally, such a therapy should guarantee, like other ones, an optimal success in the shortest period of treatment. If however too high intensities of current are utilized which are of significance for the degree of muscle stimulation and consequently for the success of the treatment, skin pains appear although in various manner in dependence on different parameters of the current. On the other hand, inflammatory skin excitations at the electrodes appear in case of a long period of application. It is therefore necessary to provide optimal pulses of current during a relative short period of treatment.
The apparatus described in the three above mentioned Patents is utilized, after a short period of acclimatization, for the simulation during the hours of sleep. However, it is now recognized that this is insufficient because, in order not to disturb the sleep, one works only with relative low current intensities, greater current intensities producing such strong muscle contractions that the patient awakens. Further, the long period of application of the electrodes leads to the already mentioned skin excitations. Moreover, the mentioned apparatus produces increasing and decreasing series of pulses which begin with a very short pulse duration of 10 .mu.s, then become longer with increasing duration of the series of pulses and amplitude and reach the greatest pulse duration of 200 .mu.s during the hold level. From the physiological point of view of the membrane, this is an unfavourable form of a series of pulses because of the very short duration of the initial pulses. Because the pulses are applied only in the domain of the lateral intercostal musculature, they are obviously not sufficient for causing the corresponding effect in the domain of the extremely important paravertebral musculature, that is immediately beside the spine and they are more particularly not able to cause also here the essential indirect excitation on the intercostal nerves. As a consequence, it was necessary to work with 2-channel stimulators as mentioned in the two indicated, successive Patents, the stimulators working either with overlapping or alternating series of pulses. In this case, two channels are each time necessary for reaching the different muscular groups of a curvature. This presents however the disadvantage that the second channel is no longer at disposal for the counter curvature of the mostly S-shaped scoliosises. This means that the muscle excitation is limited to only a part of the scoliosis. Moreover, the short pulses have the effect that only muscle fibre lying in the surface of the muscle groups are attained, these fibres having the lowest excitation threshold, and not the central zones with a high excitation threshold.
Moreover, the said apparatuses and also other known apparatuses, i.e. according to U.S. Pat. Nos. 4,102,348 and 4,539,993 work in accordance with the low frequency concept, that is with pulse repetition frequences of about 30 Hz in order not to create a fatigue of the muscle. However, it is known that a muscle which is not fatigued during training is not sufficiently trained. It is essential in this respect that recuperation pauses be provided. It has been found that the low frequency pulses feed the tonus fibres of the musculature which, although being capable of continuous working do not possess the cability of a rapid force development which would be necessary for acting on the scoliosis deformities in order to correct them.